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Add a MinNumRegs argument to MRI::constrainRegClass().

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The function will refuse to use a register class with fewer registers
than MinNumRegs.  This can be used by clients to avoid accidentally
increase register pressure too much.

The default value of MinNumRegs=0 doesn't affect how constrainRegClass()
works.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140339 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2011-09-22 21:39:31 +00:00
parent 17470bee5f
commit 91fb536a34
2 changed files with 11 additions and 7 deletions
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8
include/llvm/CodeGen/MachineRegisterInfo.h
View File

@ -215,13 +215,15 @@ public:
void setRegClass(unsigned Reg, const TargetRegisterClass *RC);
/// constrainRegClass - Constrain the register class of the specified virtual
/// register to be a common subclass of RC and the current register class.
/// Return the new register class, or NULL if no such class exists.
/// register to be a common subclass of RC and the current register class,
/// but only if the new class has at least MinNumRegs registers. Return the
/// new register class, or NULL if no such class exists.
/// This should only be used when the constraint is known to be trivial, like
/// GR32 -> GR32_NOSP. Beware of increasing register pressure.
///
const TargetRegisterClass *constrainRegClass(unsigned Reg,
const TargetRegisterClass *RC);
const TargetRegisterClass *RC,
unsigned MinNumRegs = 0);
/// recomputeRegClass - Try to find a legal super-class of Reg's register
/// class that still satisfies the constraints from the instructions using

10
lib/CodeGen/MachineRegisterInfo.cpp
View File

@ -49,15 +49,17 @@ MachineRegisterInfo::setRegClass(unsigned Reg, const TargetRegisterClass *RC) {
const TargetRegisterClass *
MachineRegisterInfo::constrainRegClass(unsigned Reg,
const TargetRegisterClass *RC) {
const TargetRegisterClass *RC,
unsigned MinNumRegs) {
const TargetRegisterClass *OldRC = getRegClass(Reg);
if (OldRC == RC)
return RC;
const TargetRegisterClass *NewRC = getCommonSubClass(OldRC, RC);
if (!NewRC)
if (!NewRC || NewRC == OldRC)
return NewRC;
if (NewRC->getNumRegs() < MinNumRegs)
return 0;
if (NewRC != OldRC)
setRegClass(Reg, NewRC);
setRegClass(Reg, NewRC);
return NewRC;
}